Note: Descriptions are shown in the official language in which they were submitted.
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POLYMER/WUCS MAT AND METHOD OF FORMING SAME
TECHNICAL FIELD AND INDUSTRIAL
APPLICABILITY OF THE INVENTION
The present invention relates generally to reinforced composite products, and
more
particularly, to a chopped strand mat that is formed of bundles of
dielectrically dried
reinforcing fibers and bonding materials. A method of forining the chopped
strand mat is
also provided.
BACKGROUND OF THE INVENTION
Glass fibers are useful in a variety of technologies. For example, glass
fibers are
commonly used as reinforcements in polymer matrices to forin glass fiber
reinforced
plastics or composites. Glass fibers have been used in the fonn of continuous
or chopped
filaments, strands, rovings, woven fabrics, non-woven fabrics, meshes, and
scrims to
reinforce polymers. It is known in the art that glass fiber reinforced polymer
composites
possess higher mechanical properties compared to unreinforced polymers. Thus,
better
dimensional stability, tensile strength and modulus, flexural strength and
modulus, impact
resistance, and creep resistance can be achieved with glass fiber reinforced
composites.
Typically, glass fibers are fonned by drawing molten glass into filainents
through a
bushing or orifice plate and applying a sizing coinposition containing
lubricants, coupling
agents, and film-forming binder resins to the filaments. The aqueous sizing
composition
provides protection to the fibers from interfilament abrasion and promotes
compatibility
between the glass fibers and the matrix in which the glass fibers are to be
used. After the
sizing composition is applied, the fibers may be gathered into one or more
strands and
wound into a package or, alternatively, the fibers may be chopped while wet
and collected.
The collected chopped strands can then be dried and cured to form dry chopped
fibers or
they can be packaged in their wet condition as wet chopped fibers.
Fibrous mats, whicli are one form of fibrous non-woven reinforcements, are
extremely suitable as reinforcements for many kinds of synthetic plastic
composites.
Dried chopped glass fiber strands (DUCS) are cominonly used as reinforcement
materials
in tliermoplastic articles. These dried chopped glass fibers may be easily fed
into
conventional machines and may be easily utilized in conventional methods, such
as dry-
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laid processes. In a conventional dry-laid process, dried glass fibers are
chopped and air
blown onto a conveyor or screen and consolidated to forin a mat. For example,
diy
chopped fibers and polymeric fibers are suspended in air, collected as a loose
web on a
screen or perforated drum, and then consolidated to form a randomly oriented
mat.
Wet chopped fibers are conventionally used in a wet-laid process in which the
wet
chopped fibers are dispersed in a water slurry wliich inay contain
surfactants, viscosity
modifiers, defoaming agents, or other chemical agents. Once the chopped glass
fibers are
introduced into the slurry, the slurry is agitated so that the fibers become
dispersed. The
slurry containing the fibers is deposited onto a moving screen, and a
substantial portion of
the water is removed to form a web. A binder is then applied, and the
resulting mat is
dried to remove the remaining water and cure the binder. The formed non-woven
mat is
an assembly of dispersed, individual glass filaments.
Dry-laid processes are particularly suitable for the production of highly
porous
mats and are suitable where an open structure is desired in the resulting mat
to allow the
rapid penetration of various liquids or resins. However, such conventional dry-
laid
processes tend to produce mats that do not have a uniform weight distribution
tluoughout
their surface areas, especially when compared to mats formed by conventional
wet-laid
processes. In addition, the use of dry chopped fibers can be more expensive to
process
than the wet chopped fibers used in wet-laid processes because the dry chopped
fibers are
generally dried and packaged in separate steps before being chopped.
For certain reinforcement applications in the formation of composite parts, it
is
desirable to form fiber mats in which the n7at includes an open, porous
structure (as in a
dry-laid process) and which has a uniform weight (as in a wet-laid process).
However,
conventional wet chopped fibers cannot be employed in conventional dry-laid
processes.
For example, wet chopped fibers tend to agglomerate or sticlc to each other
and/or the
processing equipment, which would cause the manufacturing equipment to fail
and stop
the manufacturing line. In addition, conventional dry-laid processes typically
employ an
air stream to deliver the dry chopped strands to a moving screen or foraminous
conveyor.
Wet chopped fibers cannot be dispersed in such an air stream witli sufficient
control to
obtain a mat that has a good dispersion of fibers.
Attempts have been made to dry the glass fiber strands as they are being
collected
at the winder or during an in-line process to improve the uniformity of the
handling and
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subsequent processing of the glass fibers. Sucli diying attempts have included
the use of
higli frequency dielectric systems for diying the glass strand and/or chopped
glass fibers,
some examples of wllicli are set forth below.
U.S. Patent No. 3,619,252 to Roscher discloses a inethod of coating and
impregnating glass fibers witli an aqueous elastomeric composition and then
drying the
glass fibers with high frequency electrical heating to remove substantially
all of the water
wliile leaving the elastomeric solids substantially unaffected.
U.S. Patent No. 3,619,538 to Kallenborn discloses a process and an apparatus
for
einploying high frequency electrical heating, sucli as dielectric heating, to
dry a plurality of
coated glass fibrous strands that are wet or saturated with an aqueous
elastomeric dip.
U.S. Patent No. 4,840,755 to Nalcazawa et al. describes a method and an
apparatus
for producing compacted chopped strands having a high density. The chopped
strands are
dried by heated air applied from the lower side of the chopped strands or by
high
frequency wave heating as they are mbved along a carrier plate.
U.S. Patent No. 6,148,641 to Blough et al. describes an apparatus and a method
for
producing dried, chopped strands from a supply of continuous fiber strands by
the direct
deposition of wet, chopped strands ejected from a chopping assembly into a
drying
chamber. The drying chamber can be any continuous or batch type dryer known to
one
skilled in the art such as electric, gas, ultraviolet, dielectric, or
fluidized bed dryers.
In view of the above, there exists a need in the art for a cost-effective and
efficient
process for forming a non-woven mat having a substantially unifonn weight
distribution,
and an open, porous structure that can be used in the production of reinforced
composite
parts and that utilizes wet chopped strands.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a low-loft, non-woven
chopped
strand mat that is formed of bundles of reinforcing fibers and a bonding
material. Suitable
examples of reinforcing fibers include glass fibers, wool glass fibers,
natural fibers, and
ceramic fibers. The reinforcing fibers may be present in the chopped strand
mat in an
amount of about 60 to about 90% by weight of the total fibers. It is preferred
that the
bundles of reinforcing fibers have a bundle tex of about 10 to about 500. In
preferred
embodiments, the reinforcing fibers are wet reinforcing fibers, such as wet
use chopped
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strand glass fibers, that have been substantially dried using a dielectric
diying oven. The
bonding material may be any thermoplastic or tllennosetting material having a
melting
point less than the reinforcing fibers.
It is also an object of the present invention to provide a method of forining
a low-
loft, non-woven chopped strand mat. In forining the chopped strand mat,
bundles of wet
reinforcement fibers (such as wet use chopped strand glass fibers) are
dielectrically dried
such as by passing the wet reinforcement fibers through a dielectric oven
where high
alternating frequency electrical fields dry or substantially dry the wet
reinforcement fibers.
The dried bundles of reinforcement fibers are fed by a first fiber transfer
system into a
fonning hood. A second fiber transfer system feeds a thermoplastic bonding
material into
the forming hood. The fiber transfer systems may be slaved to each other so
that a
matched ratio of bonding material to reinforcing fiber can be obtained. The
dried
reinforcement fibers and bonding material are blended together in the forming
hood by a
high velocity air stream. The mixture of dried reinforcement fibers and
bonding material
are pulled downward within the forming hood and onto a moving conveying
apparatus
with the aid of a vacuum or air suction system to form a sheet of ra.ndoinly,
but
substantially evenly distributed, bundles of dried reinforcement fibers and
bonding fibers.
The sheet is then passed through a thermal bonding system to bond the dried
reinforcement
fibers and bonding material and form the chopped strand mat. The chopped
strand mat
may be passed through a compacting system where the chopped strand mat is
compacted,
preferably to a thickness of from about 1/16 to about 1/2 inch. The chopped
strand mat
may be further processed by passing the chopped strand mat through a cooling
system and
then wound by a winding apparatus into a continuous roll for storage.
It is a fiu-ther object of the present invention to provide a method of
forming a low-
loft, non-woven chopped strand that utilizes a polymer mat as the binding
material. Wet
reinforcement fibers that have been dielectrically dried, such as in a
dielectric oven, are
deposited into a forming hood by a first fiber transfer system. Preferably,
the wet
reinforcement fibers are formed as bundles of reinforcing fibers with a bundle
tex of from
about 10 to about 500. The dried reinforcement fibers are suspended by a high
velocity air
stream generated within the forining hood. A first polymer mat is positioned
onto a
conveying apparatus and introduced into the forming hood. The dried
reinforcement fibers
are drawn downward and deposited onto the first polymer mat. The result is a
polymer
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mat having thereon a substan.tially even distribution of dried bundles of wet
reinforcement
fibers. The polymer/glass mat may then be passed through a thermal bonding
systein to
bond at least a portion of the dried reinforcement fibers and the polyiner
material forining
the first polymer mat. A second polymer mat may optionally be positioned on
the layer of
dried bundles of reinforcement fibers such that the dried bundles of
reinforcement fibers
are sandwiclied between the first and second polymer mats. The first and
second polymer
mats may be formed of the same polymers or they may be formed of different
polymers,
depending on the desired application.
It is an advantage of the present invention that the use of dielectrically
dried wet
chopped glass fibers provides a cost advantage over conventional low tex roved
fiber
products wllich are currently used in diy-laid processes. As a result, the use
of
dielectrically dried wet chopped glass fibers allows chopped strand mats to be
manufactured at lower costs.
It is another advantage of the present invention that dielectrically drying
the wet
reinforcement fibers provides an economic method of removing water from the
wet
reinforcement fibers because the wet reinforcement fibers may be quickly dried
at a low
net fiber temperature. In addition, dielectrically drying the wet
reinforcement fibers
enhances fiber-to-fiber cohesion and reduces bundle to bundle adhesion.
It is a further advantage of the present invention that in removing the water
from
the wet reinforcement fibers at lower temperatures through dielectric drying,
the chemical
reactions of the surface chemistry on the glass fibers may be reduced.
It is yet another advantage of the present invention that the use of a
dielectric oven
permits the wet reinforcing fibers to be dried with no active method of fiber
agitation.
This laclc of agitation eliminates the abrasion of fibers cominonly seen in
conventional
fluidized bed and tray drying ovens due to the high air flow velocities within
the drying
ovens and the mechanical motion of the fibrous material in the beds. In
addition, the lack
of agitation greatly increases the ability to maintain the fiber bundles.
It is also an advantage of the present invention that the dielectric oven
reduces the
discoloration of glass commonly resulting from the use of thermal drying
process
equipment.
The foregoing and other objects, features, and advantages of the invention
will
appear more fully hereinafter from a consideration of the detailed description
that follows.
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It is to be expressly understood, however, that the drawings are for
illustrative purposes
and are not to be construed as defining the limits of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The advantages of this invention will be apparent upon consideration of the
following detailed disclosure of the invention, especially when taken in
conjunction with
the accoinpanying drawings wlierein:
FIG. 1 is a schematic illustration of a chopped strand bundle according to an
exeinplaiy embodiment of the present invention;
FIG. 2 is a flow diagram illustrating steps for forining a chopped strand mat
using
wet reinforcement fibers according to one aspect of the present invention;
FIG. 3 is a schematic illustration of a process using dielectrically dried
reinforcement fibers to form a chopped strand mat according to at least one
exemplary
embodiment of the present invention; and
FIG. 4 is a schematic illustration of a forming hood according to at least one
exemplaty embodiment of the present invention.
DETAILED DESCRIPTION AND
PREFERRED EMBODIMENTS OF THE INVENTION
Unless defined otherwise, all technical and scientific terms used herein have
the
same meaning as cominonly understood by one of ordinary skill in the art to
which the
invention belongs. Altliough any methods and materials similar or equivalent
to those
described herein can be used in the practice or testing of the present
invention, the
preferred methods and materials are described herein. All references cited
herein,
including published or corresponding U.S. or foreign patent applications,
issued U.S. or
foreign patents, or any other references, are each incorporated by reference
in their
entireties, including all data, tables, figures, and text presented in the
cited references.
In the drawings, the thiclcness of the lines, layers, and regions may be
exaggerated
for clarity. It is to be noted that like numbers found throughout the figures
denote like
elements. The terms "top", "bottom", "side", and the like are used herein for
the purpose
of explanation only. It will be understood that when an element is referred to
as being
"on," "adjacent to," or "against" another element, it can be directly on,
adjacent to, or
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against the other element or intervening eleinents may be present. It will
also be
i.uiderstood that when an element is referred to as being "over" anotlier
element, it can be
directly over the other element, or intervening eleinents may be present. The
terms
"reinforcing fibers" and "reinforcement fibers" may be used interchangeably
herein. The
terins "bonding fibers" and "bonding material" may also be interchaiigeably
used. In
addition, the terins "sheet" and "mat" may be used interchangeably herein.
The present invention relates to a chopped strand mat that is formed of
bundles of
reinforcing fibers and organic bonding fibers. The chopped strand mat is a low
loft, non-
woven mat that may be used, for example, as a reinforcement in composite
articles, in
injection molding, in pultrusion processes, in structural resin injection
molding, in open
mold resin systems, in closed mold resin systems, in polymer gypsuin
reinforcement, in
polymer concrete reinforcement, in compression molding, in resin transfer
molding, and in
vacuum infusion processes.
The reinforcing fibers may be any type of organic, inorganic, or natural fiber
suitable for providing good structural qualities. Preferred examples of
suitable reinforcing
fibers include glass fibers, wool glass fibers, natural fibers, and ceramic
fibers. The
chopped strand mat may be entirely formed of one type of reinforcement fiber
(such glass
fibers) or, alternatively, more than one type of reinforcement fiber may be
used in forming
the chopped strand mat. The term "natural fiber" as used in conjunction with
the present
invention refers to plant fibers extracted from any part of a plant,
including, but not limited
to, the stem, seeds, leaves, roots, or bast. Preferably, the reinforcing
fibers are glass fibers.
The reinforcing fibers may be chopped fibers having a discrete length of about
1/2
to about 2 inches, and preferably about 3/4 to aboutl 1/2 inches. In addition,
the
reinforcing fibers may be formed of a single chop length of about 1 to about 1
1/2 inches
or a multi-chop length of fibers ranging from about 1/2 to about 2 inches. The
reinforcing
fibers may have diameters of about 10 to about 22 microns, preferably from
about 12 to
about 16 microns, and more preferably from about 11 to about 12 microns. It is
preferred
that the reinforcing fibers are formed as bundles of reinforcing fibers with a
bundle tex of
from about 10 to about 500, preferably from about 20 to about 400, and more
preferably
from about 30 to about 100. An example of a suitable chopped strand bundle is
illustrated
in FIG. 1. The chopped strand bundle 70 shown therein is formed of individual
filaments
72 having a discrete desired length 74 and desired diameter 76 as described
above.
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Although not wishing to be bound by tlieoty, it is believed that when the tex
of
each bundle reaches a sufficient amotuit, the fibers form an asseinbly of
fibrous "sticks"
that are held together by the bonding material. A chopped strand mat forined
from these
higli tex biuidles of reinforcing fibers will result in a low-loft chopped
strand mat that wets
out in a resin quickly and that will be relatively thin, especially when
coinpared to
conventional high-loft air-laid mat products. In addition, the low-loft
bundled chopped
glass fiber mats are formed of fibers packed together along the fiber axis,
which pennits
the chopped glass mat to have an increased glass content. In composite mats
such as the
chopped strand mat of the present invention, mechanical and impact performance
are
directly proportional to the glass content. Because the chopped strand mat has
an
increased glass content, it is able to provide increased mechanical and
iinpact performance
in the final products, especially when compared to the conventional high-loft
dry-laid mat
products that have dispersed fibers and a limited glass content (e.g., about
20 to about 30%
glass).
The reinforcing fibers may have varying lengths and diameters from each other
witllin the chopped strand mat, and may be present in an amount of from about
60 to about
90% by weight of the total fibers. Preferably, the reinforcing fibers are
present in the
chopped strand mat in an amount of about 80 to about 90% by weight. In a most
preferred
embodiment, the reinforcing fibers are present in an amount of about 90% by
weiglit.
The bonding material may be any thermoplastic or thermosetting material that
has
a melting point less than the melting point of the reinforcing fibers. Non-
limiting
examples of thermoplastic and thermosetting materials suitable for use in the
chopped
strand mat include polyester fibers, polyethylene fibers, polypropylene
fibers, polyetliylene
terephthalate (PET) fibers, polyphenylene sulfide (PPS) fibers, polyvinyl
chloride (PVC)
fibers, ethylene vinyl acetate/vinyl chloride (EVA/VC) fibers, lower alkyl
acrylate polymer
fibers, acrylonitrile polymer fibers, partially hydrolyzed polyvinyl acetate
fibers, polyvinyl
alcohol fibers, polyvinyl pyrrolidone fibers, styrene acrylate fibers,
polyolefins,
polyamides, polysulfides, polycarbonates, rayon, nylon, phenolic resins, and
epoxy resins.
The bonding material may be present in the chopped strand mat in an ainount of
from
about 10 to about 40% by weight of the total fibers, and preferably from about
10 to about
20% by weight. In a most preferred embodiment, the bonding material is present
in the
chopped strand mat in the in an amount of aboutl0% by weight.
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In addition, the bonding fibers may be functionalized with acidic groups, for
exainple, by carboxylating with an acid such as a maleated acid or an aciylic
acid, or the
bonding fibers may be functionalized by adding an anhydride group or vinyl
acetate. The
bonding material may also be in the form of a flalce, a gra.nule, a resin, or
a powder rather
than in the form of a polymeric fiber.
The bonding material may also be in the form of multicomponent fibers such as
bicoinponent polyiner fibers, tricomponent polyiner fibers, or plastic-coated
mineral fibers
such as thermosetting coated glass fibers. The bicomponent fibers may be
aiTanged in a
sheath-core, side-by-side, islands-in-the-sea, or segmented-pie arrangement.
Preferably,
the bicomponent fibers are formed in a sheath-core arra.ngement in which the
sheatll is
formed of first polymer fibers that substantially surround a core formed of
second polymer
fibers. It is not required that the sheath fibers totally surround the core
fibers. The first
polymer fibers have a melting point lower than the melting point of the second
polymer
fibers so that upon heating the bicomponent fibers to a teinperature above the
melting
point of the first polymer fibers (sheath fibers) and below the melting point
of the second
polymer fibers (core fibers), the first polymer fibers will soften or melt
while the second
polymer fibers remain intact. This softening of the first polymer fibers
(sheath fibers) will
cause the first polymer fibers to become sticky and bond the first polyiner
fibers to
themselves and other fibers that may be in close proximity.
The chopped strand mat may be formed by a dry-laid process, such as any of the
conventional dry-laid processes known to those of skill in the art. In
preferred
embodiments, the reinforcing fibers used to form the chopped strand mat are
wet
reinforcing fibers that have been substantially dried using a dielectric
drying oven. As
used herein, the pllrase "substantially dried" is meant to indicate that the
wet reinforcing
fibers are dry or nearly dry. In preferred embodiments, the wet reinforcement
fibers are
wet use chopped strand glass fibers (WUCS). Wet use chopped strand glass
fibers for use
as the reinforcement fibers may be formed by conventional processes known in
the art. It
is desirable that the wet use chopped strand glass fibers have a moisture
content of from 5
- 30%. It is even more preferred that the wet use chopped strand glass fibers
have a
moisture content of from about 5 to about 15%.
The use of dielectrically dried wet use chopped strand glass fibers provides a
cost
advantage over conventional low tex roved fiber products (such as rovings)
which are
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currently used in dry-laid processes. For example, wet use cliopped strand
glass fibers are
less expensive to manufacture tlian roved fibers because roved fibers require
multiple
manufacturing steps such as winding, drying, creel loading, unwinding, and
chopping to
obtain a fiber that can be used in manufacturing processes. The use of
dielectrically dried
wet use chopped strand glass fibers allows chopped strand mats to be
manufactured at
lower costs. In addition, as a roving is dried, the size on the glass fibers
tends to migrate
toward the outside of the package, which causes an uneven distribution of size
tllrougllout
the roving package. The outside of the roving package is typically removed and
discarded
as waste. The inventive chopped strand mat does not result in a migration of
size and, as a
result, reduces the amount of waste generated.
An exemplary process for foiming the chopped strand mat using dielectrically
dried reinforcement fibers is generally illustrated in FIG. 2. The process
shown therein
includes dielectrically drying the wet reinforcement fibers (10), blending the
dried
reinforcement fibers and bonding material (20), bonding the reinforcement
fibers and
bonding material (30), compacting the chopped strand mat (40), cooling the
chopped
strand mat (50), and winding the mat into a continuous roll (60).
The formation and storage of a chopped strand mat according to an exemplary
embodiment of the instant invention is depicted in FIG. 3. As illustrated in
FIG. 3, wet
reinforcement fibers 100 are introduced into a dielectric oven 110.
Preferably, these wet
reinforcement fibers are present in bundles. The dielectric oven 110 includes
spaced
electrodes that produce alternating high-frequency electrical fields between
successive
oppositely charged electrodes. The wet reinforcement fibers pass between the
electrodes
and through the electrical fields where the high alternating frequency
electrical fields act to
excite the water molecules and raise their molecular energy to a level
sufficient to cause
the water within the reinforcement fibers to evaporate.
The ainount of electrical activation and duration of time within the
dielectric oven
110 are controlled such that the reinforcement fibers that leave the
dielectric oven 110 are
substantially dry and non-tacky. The duration of drying time may be controlled
through a
closed loop feed back of the power draw that the dielectric oven 110 is
experiencing to
determine when the reinforcing fibers are substantially dry. In exemplary
embodiments,
greater than about 70% of the free water (water that is external to the
reinforcement fibers)
is removed. Preferably, however, substantially all of the water is removed by
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oven 110. It should be noted that the pluase "substantially all of the water"
as it is used
herein is meant to denote that all or nearly all of the free water is removed.
The dielectric oven 110 perinits the wet reinforcing fibers 100 to be quickly
dried
at a low net fiber temperature. The net fiber temperature is dependent upon
the chemistiy
of the size coating the glass fiber, which, in turn, is dependent upon the
intended
application. Therefore, the dielectric oven 110 provides an economic inethod
of removing
water from the wet reinforcement fibers 100. In addition, dielectrically
drying the bundles
of wet reinforcement fibers enllances fiber-to-fiber cohesion a.nd reduces
bundle-to-bundle
adhesion. The dielectric energy penetrates the wet bundles of chopped fibers
evenly and
causes the water to quickly evaporate, helping to keep the wet glass bundles
separated
from each other. Further, the dielectric drying of the size on the chopped
fibers also assists
in filimentizing the bundles in the chopped strand mat during subsequent
processing steps
(such as molding the chopped strand mat) to form an aesthetically pleasing
finished
product. The dielectric drying lightly cures the size so that even
filimentation can occur.
By removing the water from the wet reinforcement fibers at lower temperatures,
the chemical reactions of the surface chemistry (e.g., size) may be reduced.
Sizing
compositions may contain a variety of components, depending on the application
of the
fibers. As one example, an epoxy fihn forming agent may be utilized in the
size applied to
the glass fibers in order to provide compatibility with epoxy resin systems.
In
conventional dry-laid processes, all or nearly all of the epoxy functional
groups within the
film forming agents in the size composition are reacted due to the extended
drying time
and high temperatures typical of conventional thermal drying processes.
However, by
dielectrically drying the size on the glass fibers at a lower temperature and
for a shorter
time period, active epoxy functional groups remain imbedded in the size on the
glass.
Further, the lower temperature of the dielectric oven and shorter drying time
needed to dry
the size reduces the discoloration of glass that commonly results from the use
of thermal
drying process equipment.
The dielectric oven 110 permits the wet reinforcing fibers 100 to be dried
with no
active method of fiber agitation as is conventionally required to remove
moisture from wet
fibers. This lack of agitation reduces or eliminates the attrition or abrasion
of fibers as is
commonly seen in conventional fluidized bed and tray drying ovens due to the
high air
flow velocities within the ovens and the mechanical motion of the fibrous
material in the
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beds. In addition, the laclc of agitation greatly increases the ability of the
dielectric oven
110 to maintain the fibers in bundles and not filamentize the fiber strands as
in the
aggressive conventional tlzermal processes.
Once the dried reinforcement fibers (such as dried WUCS fibers) leave the
dielectric oven 110, they are fed by a first fiber transfer system 120 into a
forming hood
300. As used herein, the tenn "dried reinforcement fibers" is meant to denote
reinforcement fibers that have all of the free water removed or nearly all of
the free water
removed. The first fiber transfer system 120 inay be any kind of loss-in-
weight or
continuous weigh feeding or dispensing device that feeds the dried fibers (not
shown) into
the forming hood 300 at a controlled rate.
The bonding materia1200, typically present in the form of a bale of fibers, is
fed
into an opening system 210 to at least partially open and/or filamentize
(individualize) the
bonding fibers 200. The opening system 210 is preferably a bale opener, but
may be any
type of opener suitable for opening the bales of bonding fibers 200. The
design of the
openers depends on the type and physical characteristics of the fiber being
opened.
Suitable openers for use in the present invention include any conventional
standard type
bale openers with or witliout a weighing device. The weighing device serves to
continuously weigh the partially opened fibers as they are passed through the
bale opener
to monitor the amount of fibers that are passed onto the next processing step.
The bonding
fibers 200 exiting the opening system 210 are then fed into a second fiber
transfer system
220 that feeds the bonding fibers 200 to the forming hood 300. The fiber
transfer system
120 may be slaved to the fiber transfer system 220 to provide a matched ratio
of bonding
material to reinforcing fiber.
In alternate embodiments where the bonding fibers are in the form of a flake,
granule, or powder, the opening system 210 and second fiber transfer system
220 may be
replaced with an apparatus suitable for distributing the flalces, powders, or
granules to the
forming hood 300 so that these resinous materials may be mixed with the dried
reinforcement fibers (not shown) in the forming hood 300. A suitable
distribution
apparatus would be easily identified by those of skill in the art.
The bundles of dried reinforcement fibers and the bonding fibers 200 are
blended
together within the forming hood 300. An exemplary embodiment of a forming
hood 300
is illustrated in FIG. 4. In preferred embodiments, the fibers are blended in
a high velocity
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air stream generated within the forining hood 300 sucll as by a fan (e.g., a
burster fan). It
is desirable to distribute tlie buiidles of dried reinforcing fibers and
bonding fibers 200 as
uniforinly as possible within the air stream. The ratio of dried reinforcing
fibers and
bonding fibers 200 entering the forining hood 300 may be controlled by the
weight feed
rate at which the fibers are passed through the first and second fiber
transfer systems 120,
220. For exainple, the control of fibers tlirough the first and second fiber
transfer systems
120, 220 may be achieved through loss-in-weight vibratory feeders such as a
vibrator pan
or weigh belt. In the exemplaiy einbodiment depicted in FIG. 4, the fiber
transfer systems
120, 220 are combinations of a dispensing unit 125, 225 and a vibratoiy feeder
130, 230
respectively. The ratio of dried reinforcing fibers to bonding fibers 200
present in the air
stream is preferably 90:10 to 60:40, dried reinforcement fibers to bonding
material 200
respectively.
The mixture of the dried reinforcement fibers and bonding fibers 200 are
pulled
downward within the forming hood 300 and onto a moving conveying apparatus 310
with
the aid of a vacuum or air suction system 320 to form a sheet of randomly, but
substantially evenly distributed, bundles of dried reinforcement fibers and
bonding
inateria1200. The conveying apparatus 310 may be any suitable conveyor
identified by
one of skill in the art (e.g., a foraminous conveyor). The sheet may then be
passed through
a thermal bonding system 400 to bond the dried bundles of reinforcement fibers
and
bonding fibers 200. In thermal bonding, the tliermoplastic properties of the
bonding fibers
200 are used to form bonds with the dried reinforcement fibers upon heating.
The sheet
contains a substantially uniform distribution of dried reinforcing fibers and
bonding fibers
210 at a desired ratio and weight distribution. The uniform or substantially
uniform
distribution of fibers provides improved strength as well as improved
acoustical and
thermal properties to the chopped strand mat 450. As used herein, the phrases
"substantially uniform distribution of fibers" and "substantially evenly
distributed fibers"
are meant to denote that the fibers are uniformly or evenly distributed or
nearly unifonnly
or evenly distributed.
In the thermal bonding system 400, the sheet is heated to a temperature that
is
above the melting point of the bonding material 200 but below the melting
point of the
dried reinforcement fibers. When bicomponent fibers are used as the
reinforcement fibers
200, the temperature in the thermal bonding system 400 is raised to a
temperature that is
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above the melting point of the sheatli fibers, but below the melting point of
the
reinforcement fibers. Heating the bonding fibers 200 to a temperature above
their melting
point, or above the melting point of the sheatll fibers in the instance wliere
the bonding
fibers 200 are bicomponent fibers, causes the bonding fibers 200 (or sheath
fibers) to
become adhesive and bond the bonding fibers 200 and dried btmdles of
reinforcing fibers.
If the bonding fibers 200 coinpletely melt, the melted fibers may encapsulate
dried bundles
of reinforcement fibers. As long as the teinperature within the thermal
bonding system
400 is not raised as high as the melting point of the reinforcing fibers
and/or core fibers,
these fibers will remain in a fibrous forin within the therinal bonding
systern 400 and
chopped strand mat 450.
The thermal bonding system 400 may include any known heating and bonding
method known in the art, such as oven bonding, infrared heating, hot
calendaring, belt
calendaring, ultrasonic bonding, microwave heating, and heated drums.
Optionally, two or
more of these bonding methods may be used in combination to bond the fibers in
the sheet.
The temperature of the thermal bonding system 400 varies depending on the
melting point
of the bonding fibers 200 used and whether or not bicomponent fibers are
present in the
sheet. However, the temperature within the thermal bonding system may be about
200 to
about 350 C. The chopped strand mat 450 that emerges from the thermal bonding
system
400 contains a uniform or nearly uniform distribution of bonding fibers 200
and bundles of
dried reinforcement fibers.
The chopped strand mat 450 may be passed through a compacting system 500
where the mat is compacted, preferably to a thickness of about 1/16 to about
1/2 inch
(about 0.158 to about 1.27 cm). The compacting system may be a series of
rollers or a
single compaction roll set. The compaction rolls may include a set of chrome
coated rolls
including a gap control system with chilled water circulating through the
rolls to keep the
surface at a temperature ranging from about 50 to about 70 F.
The chopped strand mat 450 may also be passed through a cooling system 600.
The cooling system may include a conveyor and a drive, such as a motor, to
move the
conveyor. A blower apparatus (not illustrated) may be located below the
conveyor to
generate suction and pull air through the chopped strand mat 450, e.g., from
the top to the
bottom. The air is preferably drawn in at the ambient temperature and is used
to drive the
temperature of the chopped strand mat 450 to room temperature. Alternatively,
the air
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may be drawn tluough a cooling coil (not illustrated) to lower the
teinperature of the air
and increase the cooling effect on the chopped strand mat 450. The chopped
strand mat
450 may then be wouud by a winding apparatus 700 onto a continuous roll (not
shown) for
storage for later use. Any conventional winding apparatus is suitable for use
in the instant
invention. The clzopped strand mat 450, as well as the glass polymer m.at
described below,
may be utilized in a number of non-structural acoustical applications such as
in appliances,
in office screens and partitions, in ceiling tiles, in building panels, and in
semi-structural
applications such as, for example, headliners, hood liners, floor liners, trim
panels, parcel
shelves, sunshades, instrument panel structures, door inners, or wall panels
or roof panels
of recreational vehicles.
In an alternate embodiment (not illustrated), wet reinforcement fibers that
have
been dielectrically dried as described above are deposited into the forming
hood 300, such
as by the first fiber transfer system 120, and suspended by the high velocity
air stream
generated within the forming hood 300: Preferably, the wet reinforcement
fibers are
formed as bundles with a bundle tex of 10 to 500. The bundles of wet
reinforcement fibers
200 may be passed tluough a dielectric oven 110 or otlzer apparatus that
generates
electrical fields and dries the wet fibers. The dried bundles of wet
reinforcement fibers
may then be transferred to the forming hood 300. A first polyiner mat (not
illustrated) may
be placed onto the conveying apparatus 310 and introduced into the forming
hood 300 at
entrance 350 (depicted in FIG. 4). The first polymer mat may be a mat of
randomly
oriented polymer fibers. Suitable polymer fibers include, but are not limited
to, polyester
fibers, polyethylene fibers, polypropylene fibers, polyetliylene terephthalate
(PET) fibers,
polyphenylene sulfide (PPS) fibers, polyvinyl chloride (PVC) fibers, ethylene
vinyl
acetate/vinyl chloride (EVA/VC) fibers, lower alkyl acrylate polymer fibers,
acrylonitrile
polymer fibers, partially hydrolyzed polyvinyl acetate fibers, polyvinyl
alcohol fibers,
polyvinyl pyrrolidone fibers, styrene acrylate fibers, polyolefins,
polyamides, polysulfides,
polycarbonates, rayon, nylon, phenolic resins, and epoxy resins.
The dried bundles of wet reinforcement fibers are drawn downward and deposited
onto the first polymer mat with the aid of a vacuum or other type of suction
apparatus.
The result is a polymer mat having thereon a substantially even distribution
of dried
bundles of wet reinforcement fibers. The polymer/glass mat may then be passed
through
the thermal bonding system 400 to bond the dried bundles of reinforcement
fibers and the
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polynler material forming the first polynler mat. The teinperature within the
thermal
bonding system 400 is variable aiid depends upon the polymer component(s)
forining the
polyiner mat. The temperature is a temperature that is high enough to at least
partially melt
the polymer material(s) in the polyiner mat and bond the dried wet
reinforcement fibers
and polyiner material to forin a polymer/glass mat. The polymer/glass mat may
then be
compacted, cooled, and rolled as described above.
A second polyiner mat (not shown) may be positioned on the layer of dried
bundles
of wet reiiiforcement fibers such that the dried bundles of reinforcement
fibers are
sandwiched between the first and second polyiner mats. The first and second
polymer
mats may be formed of the same polymers or they may be formed of different
polymers,
depending on the desired application. The second polymer mat may be affixed to
the
reinforcing fibers by tllennal bonding as described above.
Having generally described this invention, a further understanding can be
obtained
by reference to certain specific examples illustrated below wllich are
provided for purposes
of illustration only and are not intended to be all inclusive or limiting
unless otherwise
specified.
Examples
Example 1 - Bundle Integrity
A sizing composition according to Table 1 was mixed and applied with a
cylindrical applicator roll to 13 m fibers at a glass bushing throughput of
70 pounds per
hour with a tip plate of 2052 tips.
Table 1
Material % Input Fraction g/100 g As
Solids Fraction Received
PD-166(a 54.5 0.53 0.585 280.79 515.22
Acetic Acid 100 0.006 0.007 3.18 3.18
A-1100,b) 58.0 0.015 0.016 7.95 13.7
PVP K-90( ) 22.0 0.33 0.364 174.83 794.7
Emery 50.0 0.025 0.028 13.25 26.49
6760L(d)
D.M. Water 0 14646.71
Total 0.906 1.0 480.0 16000.00
(a) PD-166 is a polyvinyl acetate emulsion from HB Fuller.
(b) A-1100 is an aminosilane available from General Electric Silicones
Division.
(c) PVP K-90 is a polyvinylpyrrolidone solution from International Specialty
Products.
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(d) Emeiy 6760 L is a polyethylenimine-fatty acid lubricant from Cognis.
The glass strand was divided into 16 sections to give a strand tex of
approximately
40 tex. The strand was chopped witli a CB 73 chopper into 11/a inch (3.175 em)
lengths
and deposited into a plastic tub. The chopped strands were then dried in a PSC
stray field
RF (dielectric) oven from a moisture content of approximately 15% to an
approximate 0%
moisture content at about 301b/hr. The resulting mass of bundles was easily
divided
(broken) into individual bundles of fibers. The moisture content was
determined to be less
than 0.5% by weight. The individual bundles were characterized as displaying
excellent
bundle stiffness.
Approximately 300 g of the bundles were then transferred by hand into a
"Preformer" (an enclosed box with a large downdraft of air used to make glass
mats called
preforms). This amount was sufficient to give an areal density of about 1
ounce per square
foot. E-240-8 mat binder (a ground-powdered thermosetting polyester binder
with benzoyl
peroxide catalyst available from AOC) was sprinkled by hand onto the mat. The
mat was
transferred into a 450 F forced air oven for 10 minutes. The mat was removed
and cooled.
The mat was determined to display excellent bundle integrity and strength.
Example 2- Dielectric Drying and Air Laid Mats
A sizing composition according to Table 2 was mixed and applied with a
cylindrical applicator roll to 16 m fibers at a glass bushing througllput of
70 pounds per
hour with a tip plate of 2052 tips.
Table 2
Material % Input Fraction g/100 g As
Solids Fraction Received
HP3-02(a) 32.0 0.75 0.939 302.44 945.13
Acetic Acid 100.0 0.006 0.008 2.420 2.42
A-1100( ) 58.0 0.0375 0.047 15.12 26.07
K-12( ) 100.0 0.005 0.006 2.02 2.02
D.M. Water 0 0.00 6024.36
Total 0.7985 1.0 322 7000.00
(a) HP3-02 is a polyurethane dispersion in water from Hydrosize, Inc.
(b) A-1100 is an aminosilane available from General Electric Silicones
Division.
(c) K-12 is a polyethylenimine-fatty acid lubricant available from AOC.
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The glass strand divided into 16 sections to give a strand tex of
approximately 70
tex. The stra.nds were chopped witli a CB 73 chopper into 11/a inch lengths.
The chopped
fibers were deposited into a plastic tub and dried in a PSC stray field RF
(dielectric) oven
from a moisture content of approximately 15% to an approximate 0% moisture
content at
about 30 lb/lir. The resulting bundle mass was easily brolcen into individual
bundles. The
moisture content was determined to be less than 0.5% by weight. The bundles
were placed
into plastic bags. The bags were then inverted to deterinine how well the
fiber bundles
dispersed from each other and how well the bundles flowed past each other. A
visual
inspection determined that the individual bundles flowed very easily and were
well
dispersed.
Approximately 300 g of the bundles were transferred by hand into a "Preformer"
(an enclosed box with a large downdraft of air used to make glass mats called
preforms).
This amount was sufficient to give an areal density of about 1 ounce per
square foot. E-
240-8 mat binder (a ground-powdered thermosetting polyester binder with
benzoyl
peroxide catalyst available from AOC) was sprinkled by hand onto the inat. The
mat was
transferred into a 450 F forced air oven for 10 minutes. The mat was removed
and cooled.
The chopped strand mat displayed excellent bundle integrity and strength.
The invention of this application has been described above both generically
and
with regard to specific einbodiments. Although the invention has been set
fortli in what is
believed to be the preferred embodiments, a wide variety of alternatives known
to those of
skill in the art can be selected within the generic disclosure. The invention
is not
otherwise limited, except for the recitation of the claims set forth below.
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